Study Questions:

Are long working hours a risk factor for incident coronary heart disease (CHD) and stroke?

Methods:

The authors reviewed published studies through a systematic review of PubMed and Embase from inception to August 20, 2014. Unpublished data were obtained from 20 cohort studies from the Individual-Participant-Data Meta-Analysis in Working Populations (IPD-Work) Consortium and open-access data archives. Cumulative random-effects meta-analysis was used to combine effect estimates from published and unpublished data.

Results:

A total of 25 studies were included from 24 cohorts in Europe, the United States, and Australia. The meta-analysis of CHD comprised data for 603,838 men and women who were free from CHD at baseline; the meta-analysis of stroke comprised data for 528,908 men and women who were free from stroke at baseline. Follow-up for CHD was 5.1 million person-years (mean 8.5 years), in which 4,768 events were recorded, and for stroke was 3.8 million person-years (mean 7.2 years), in which 1,722 events were recorded. In cumulative meta-analysis adjusted for age, sex, and socioeconomic status, compared with standard hours (35-40 hours per week), working long hours (≥55 hours per week) was associated with an increase in risk of incident CHD (relative risk [RR], 1.13; 95% confidence interval [CI], 1.02-1.26; p = 0.02) and incident stroke (1.33; 95% CI, 1.11-1.61; p = 0.002). The excess risk of stroke remained unchanged in analyses that addressed reverse causation, multivariable adjustments for other risk factors, and different methods of stroke ascertainment (range of RR estimates, 1.30-1.42). There was a dose–response association for stroke, with RR estimates of 1.10 (95% CI, 0.94-1.28; p = 0.24) for 41-48 working hours, 1.27 (95% CI, 1.03-1.56; p = 0.03) for 49-54 working hours, and 1.33 (95% CI, 1.11-1.61; p = 0.002) for 55 working hours or more per week compared with standard working hours (ptrend < 0.0001).

Conclusions:

Employees who work long hours have a higher risk of stroke than those working standard hours; the association with CHD is weaker. These findings suggest that more attention should be paid to the management of vascular risk factors in individuals who work long hours.

Perspective:

Increase in strokes associated with longer hours worked is independent of gender and geographical region. While the impact of very long (>50-55) hours worked was modest on CHD events (increase 13%) compared to incident strokes (increase 33%), the risk of nonfatal and fatal CHD was greater in persons with a low socioeconomic (SES) despite those with higher SES being more likely to work long hours. Several studies have shown that the cardiovascular event rate relationship with long work hours is related to a decrease in locus of control (within the job), which is also more likely in persons with a low SES.